That and there is another time when BA threatens a passenger jet in order to force Billy to stop fighting and leave. Up until then, it was a back and forth. So it seems that BA's aggressiveness has not given him any noticeable advantage over Billy in a clean fight.

Yeah, Adam's ruthlessness hasn't obviously given him much of an edge against Billy, if one at all. Superman did once say that Adam hit harder though, and Adam has looked more impressive fighting other heroes than I think Billy typically would.

It is possible that Billy subconsciously fights harder against Adam than he does generally, due to his knowledge of Adam's powers and temperament. It makes sense that he'd hold back less against Adam than he would against a fellow hero like Superman. That's just my speculation though.